Third, we present electron observations made by the NASA spacecraft Mariner 10 during its first Mercury flyby on 29 March 1974 [1]}. In Fig. REF  we show magnetic field (upper panels) and electrons (bottom panels) data for the inbound (left) and outbound (right) magnetopause crossings. In particular, we observe a bimodal character of the electron energy distribution during the crossing (bottom panels), with one ambient electron population around 50-70 eV and a second energized population around 300-500 eV. This is consistent with the
signatures expected for LHDI-accelerated electrons.
Although these observations
suggest that the LHDI might play a role in the electron energization at Mercury's Magnetopause,
the Mariner 10 data cannot unambiguously confirm this hypothesis because of the lack of electric field observations. Moreover, the low time resolution of Mariner 10 electron measurements (1/6 \(s^{-1}\) ), the narrow energy range (13.4-687 eV) and the lack of a statistically significant number of crossings make the Mariner 10 observations prevent from a conclusive evidence of LHDI-accelerated electrons at Mercury's magnetopause.
